Tribukait A, Eiken O, Lemming D, Levin B. Use of an adjustable hand plate in studying the perceived horizontal plane during simulated flight. Aviat Space Environ Med 2013; 84:739–45. Background: Quantitative data on spatial orientation would be valuable not only in assessing the fidelity of flight simulators, but also in evaluation of spatial orientation training. In this study a manual indicator was used for recording the subjective horizontal plane during simulated flight. Methods: In a six-degrees-of-freedom hexapod hydraulic motion platform simulator, simulating an F-16 aircraft, seven fixed-wing student pilots were passively exposed to two flight sequences. The first consisted in ?a number of coordinated turns with visual contact with the landscape ?below. The visually presented roll tilt was up to a maximum 67°. The second was a takeoff with a cabin pitch up of 10°, whereupon external visual references were lost. The subjects continuously indicated, with the left hand on an adjustable plate, what they perceived as horizontal in roll and pitch. There were two test occasions separated by a 3-d course on spatial disorientation. Results: Responses to changes in simulated roll were, in general, instantaneous. The indicated roll tilt was approximately 30% of the visually presented roll. There was a considerable interindividual variability. However, for the roll response there was a correlation between the two occasions. The amplitude of the response to the pitch up of the cabin was approximately 75%; the response decayed much more slowly than the stimulus. Discussion: With a manual indicator for recording the subjective horizontal plane, individual characteristics in the response to visual tilt stimuli may be detected, suggesting a potential for evaluation of simulation algorithms or training programs.